Aircraft auxiliary power units have been, for example, gas turbines located in the aft fuselage. The turbines provide electrical power and compressed air on the ground, as well as in flight. They drive the air conditioning packs of the environmental control system, air driven hydraulic pumps and the starters for the wing engines. They also provide power for wing engine starts during flight, up to 14,000 feet. The auxiliary power unit generators provide electrical power to the airplane system when the main engine generators are not operating.
Typically, the air supply to the gas turbines enters through a 20.degree. ramp inlet positioned in the tail cone. In the prior art, the inlets were generally of the flush type and did not provide sufficient pressure recovery to consistently start and/or operate the auxiliary power units in flight, such starting being required up to altitudes as high as 25,000 feet. The inability to start was due to thick boundary layers on the aft body; the boundary layers vary in thickness from five to twenty inches, for example.
Ogee wing defectors have been used to overcome the prior art problems, but they cause an excessive amount of drag.